This is actually a semi-brilliant adaptation of sonic's gameplay in a 3D world. DOOM was already about running around at the speed of sound, and the addition of Sonic-style slippery momentum works well. Let me clarify that statement, it's A GOOD ADAPTATION of the same slippery momentum of the 16-bit Sonic games, for good and for bad. The DOOM engine also looks great when handling the retro aesthetics (like we said before, the 3D in DOOM is technically a complicated 2D rendering). This is a fully functional game with various gameplay styles and characters and a much better outlet for obsessive Sonic fandom than disturbingly erotic Christian artwork.
This is a loooooooong video of the game, skip around and see JUST how far they stretch the limits of the DOOM tech and see how many different types of enviroments they can create.
Notice there's a LOT of instakills, a lot of bottomless pits and traps that are easy to slip into, but that's SONIC at the end of the day. Even for just curiosity's sake, take a look and see what it feels like when you gotta go fast.
Download it here.
If you're feeling a little nostalgic for the time period when Ghostbusters was a fun movie/toy franchise and not a topic you have to actively avoid at Thanksgiving, you might get a rush out of this semi-conversion that gives you a first-person perspective on such famous locations as the Library, the firehouse, and the rooftop battle with Gozer the Gozerian. Also worth mentioning is how they replaced the bloody face of the doomguy with a increasingly-annoyed Harold Ramis.
This project seems to be abandoned, but if you want to blast the Stay-Puft Marshmallow Man while listening to a MIDI version of Ray Parker, this is worth playing around with: